The present invention relates to a safety belt retractor. A previously known safety belt retractor comprises a takeup shaft, an inertia member mounted on the takeoff shaft for rotation relative thereto, and a clutch mechanism for bringing a pawl into engagement with a ratchet wheel affixed to the takeup shaft, thereby to prevent the takeup shaft from rotating when it and the inertia member are rotated relative to each other due to a difference between the speeds of rotation thereof. The known retractor operates effectively in its main function of stopping the belt from unwinding from the reel in a collision but occasionally malfunctions when the belt is undone from a buckle and is rewound on the takeup shaft for storage. The malfunction results in the inability to pull the belt from the retractor, a problem known as an "end lock."
The end lock in this retractor is caused by the unusual concurrence of several events, namely (1) inertial rotation of the inertia member after the takeup shaft has ceased its spring-loaded rotation upon completion of the belt winding, (2) actuation of the clutch mechanism due to such inertial rotation, (3) rotation of the takeup shaft in an opposite direction, that is, a belt-unwinding direction, due to reaction or rebound thereof, and (4) rotation of the inertia member in an opposite direction which is occasioned by the reverse rotation of the takeup shaft. When these events all occur, the clutch mechanism causes the pawl to engage the ratchet wheel, and keeps the pawl and the ratchet wheel in the engaging condition. Under such condition, the takeup shaft is prevented from rotating in the direction to allow the belt to unwind, so the belt, therefore, cannot be pulled out.
The safety belt retractor of the conventional design is also occasionally bothersome to the user, because when the vehicle incorporating the safety belt retractor is subjected to sudden shocks, the pawl can engage the ratchet wheel and prevent the safety belt from being pulled out, for example, when the user tries to lean forward.